1. Field of the Invention
The present invention relates to a conical disk pair for a belt-driven conical-pulley transmission.
2. Description of the Related Art
Belt-driven conical-pulley transmissions, also known as CVT transmissions, such as are employed in motor vehicles, for example, include two pairs of conical disks that are encircled by an endless torque-transmitting means, for example a plate link chain. By changing the spacing between the conical disks of each conical disk pair in opposite directions, the transmission ratio of the transmission can be varied continuously. Advantageously, a conical disk pair, preferably the one on the power input side, includes an integrated torque sensor with which the torque delivered by a drive engine is detected, and an axially-directed pressure between the conical disks of the corresponding disk pair is changed in accordance with the torque.
Such an inherently known conical disk pair will be described below on the basis of FIGS. 1 and 2, which each show a longitudinal section through a conical disk pair, but with the sensing piston located in different positions.
As shown in FIG. 1, a pair of conical disks of a belt-driven conical-pulley transmission includes an input shaft 10 that is made in one piece with an axially fixed disk 12. Situated on shaft 10, axially movable but connected to the shaft 10 in a rotationally fixed connection, is an axially movable disk 14. An endless torque transmitting means (not shown) circulates between the conical surfaces of disks 12 and 14 on the input side of the transmission and the conical surfaces of another pair of conical disks (not shown) that are on the output side of the transmission.
On the back side of movable disk 14 in its radially outer area, a cylindrical ring 16 having two radially spaced walls is rigidly attached, within which a piston 18 operates, so that on the right side of piston 18, as viewed in FIG. 1, a first pressure chamber 20 is formed. Chamber 20 is subjected to hydraulic pressure through radial bores 22 bored in axially movable disk 14, an annular chamber 24 between axially movable disk 14 and shaft 10, a radial bore 26, and an axial bore 28 bored in shaft 3, which hydraulic pressure is changeable to adjust the transmission ratio.
Piston 18, which is of annular form, is rigidly connected to a support ring 30 that is cup-shaped, and which is rigidly connected to shaft 10. On the inner side of support ring 30 is an annular component 34 having a shaped surface 32, and which is rigidly connected to the shaft 10.
Also situated within the support ring 30 is an axially movable, annular sensing piston 36 that includes a seal that acts against the circumferential outer surface of shaft 10, and a seal that acts against an inner circumferential surface of annular component 34. Sensing piston 36 is designed with a projection directed toward axially movable disk 14, on the back face of which shaped surfaces 38 are formed that constitute opposed surfaces to the shaped surface 32. Situated between shaped surfaces 32 and 38 are rolling elements, in the illustrated example balls 40.
Between sensing piston 36 and axially movable disk 14 a second pressure chamber 42 is formed that can be subjected to hydraulic pressure through a supply line 44 in shaft 10, the hydraulic fluid being removable through a drain line 46 that is also formed in shaft 10.
The effective cross-sectional area of the inflow opening 48 that leads into the second pressure chamber 42 is determined by the axial position of axially movable disk 14. The open area of the outflow opening 50 leading out of the second pressure chamber 42 is determined by the position of sensing piston 36. Sensing piston 36 includes axial arms 52 that extend through apertures in the support ring 30. Axial arms 52 are preferably spaced at equal intervals in the circumferential direction. The radially outer surfaces of the axial arms 52 are provided with axially and radially outwardly extending teeth that mesh with inner teeth of an input wheel 54, which is supported and is substantially axially immovable on an external shell 56 of a bearing which is designated in its entirety as 58.
The construction and the function of the conical disk pair described so far are known and will therefore be explained only briefly.
When there is a torque from the rotationally driven input wheel 54 acting on axial arms 52 of sensing piston 36, that torque is transmitted via the shaped surfaces 38, the balls 40, and the shaped surfaces 32 to the support ring wall 30, and thereby to the shaft 10. The shaped surfaces 32, 38 are designed so that as the torque increases sensing piston 36 moves to the right as viewed in FIG. 1, so that the outflow opening 50, which is not completely covered by the sensing piston in the basic or starting position of the conical disk pair as shown in FIG. 1, is increasingly closed. FIG. 2 shows the arrangement of FIG. 1 with very high torque, at which the sensing piston 36 is shifted as far as possible to the right and completely covers the outflow opening 50. As the effective size of the outflow 50 becomes smaller, the pressure in second pressure chamber 42 increases, so that a pressure that is a function of the input torque acts against axially movable disk 14.
Advantageously, to support the free ends of the arms 52, a support ring 60 is provided that is in contact with the radially inner sides of the end areas of the arms 52 and urges them outward, so that the radially-outwardly-extending teeth of the arms are forced into secure meshing engagement with the inner teeth of the input wheel 54.
The arms 52 are advantageously formed on an annular element that is welded to the sensing piston 36, as shown, and from which they project axially. In that way the welding of the arms relative to the annular element relieves them of bending forces that act directly on the arms in a circumferential direction.
A peculiarity of conical disk pairs having an integrated torque sensor, as described above, consists in the fact that torque oscillations can occur through the entire system, depending upon mass inertias and rigidities in the power train of a vehicle, the damping of the overall system, and of support gradients over the transmission ratio. Such torque oscillations cause comfort problems, or possibly even an overloading of the transmission. The problems become more severe as the maximum permissible torque of a drive engine increases.
An object of the present invention is to provide a remedy for the above-identified problem.